The other extreme - very LOW chlorine demand!

[doncaruana]

Okay...this is now too good... After shocking a couple of weeks ago, my water is simply spectacular. I mean crystal clear. My CYA is at 40 while I wait for the FC to come down. When I quit shocking about 12 days ago, it was at around 19. This morning it's still only at 6.5! And we've had a few pretty sunny days and swam a fair amount. It got to about 10 maybe a week ago and is just crawling downward. We swam a couple of hours yesterday and got some sun, yet only lost 0.5.

It was 90 and mostly sunny today, but I didn't check it this evening (I usually just check in the morning). I've even taken to running the pump for 30-40 minutes before checking, just to make sure it's stirred up good.

So...what sort of freakish thing is going on with this? I don't want to look a gift horse in the mouth, it's just crazy...

 

[pwrstrk]

I think your fine. Don't sweat it.


Sent from my iPhone using Tapatalk.

 

[Charlie_R]

Granted, my pool is much smaller, but there are days that I don't need to dose with bleach, and my CYA is only 30 currently. Pool is shaded most of the day, with only a few hours in the early afternoon that I get full sun. I also try to keep my FC on the high end of the charted level.

What you currently have is a great thing. Do keep testing daily. Don't expect it to last forever.

Congrats for having a great pool!

 

[JasonLion]

Odds are your CYA level is actually a little higher than you think it is, or your pool is really well shaded.

Regardless, enjoy

 

[doncaruana]

Odds are your CYA level is actually a little higher than you think it is, or your pool is really well shaded.

Regardless, enjoy

That's what I was thinking, so I keep testing it to see if it's higher. Keep getting the same result!

I get direct light on the entire pool from probably around 10am to 6 or so. Then some trees start obscuring part of it.


As a side note, I keep making comments to my family..."Who takes care of your water? They do an excellent job! This water is amazing!"
The responses---
My daughter (with an occasional eye-roll): "You do daddy!"
My wife (with a crooked smile): "The pool boy."

 

[chem geek]

Are you sure your Intellichlor IC40 is really turned off?

 

[doncaruana]

Are you sure your Intellichlor IC40 is really turned off?

Not only was it turned off, I set the percentages to 0. Yesterday I actually decided to turn it back on at 5% on the offhand chance that having it off and at 0 would make it operate in some weird default mode. That will only add 0.2/day (the pump is running 10 hours/day right now). Lo and behold, this morning the FC is at 3.2 (I used the 25ml) after being at 6.5 yesterday. So...maybe my hunch was right?

In any case, quick basic question - if I added CYA (liquid) this morning, it should bump it up to around 60-65. Will that additional CYA now bond to an extra amount of FC, taking my actual FC down farther? Is that the way that works? So should I bump up the IC40 a little extra today to feed the CYA *and* the sun?

 

[chem geek]

That's weird that having it "off" and with 0% might have had it actually on, though it would be consistent with what you were seeing.

A higher CYA level for the same FC level will lower the active chlorine level. For your saltwater chlorine generator (SWCG) pool, just make sure that your FC is at least 5% of the CYA level at all times. Even with a proportionately higher FC level, a higher CYA level will result in a lower absolute FC loss per day which is why we generally recommend 70-80 ppm CYA for SWCG pools. See Recommended Levels and the Chlorine / CYA Chart.

 

[Cloudbusting]

well, what's the water temperature? with cover and low water temp I observed very low chlorine demand in the past (pre swg days) as well.

Just touching the swg panel with transformer inside tells me if it's working/generating or not.

 

[scott.MI]

I know chem geek posted a breakdown of chlorine demand from swimmers in a pool and it was quite low. Nothing compared to a hot sweaty small hot tub. He has too many posts for me to find it, but basically you needed quite a few swimmers for an hour just for a 1ppm demand.

 

[chem geek]

One person-hour of swimming in 10,000 gallons is around 0.1 ppm FC chlorine demand assuming no one intentionally urinates. One cup of urine is equivalent to 6-7 person-hours of swimming. So in most residential pools, bather load can be ignored unless you have a swim party or have kids (or others) urinating in the pool).